A variety of roll over vent valves are well known, examples thereof being described inter alia in U.S. Pat. Nos. 5,313,977 and 5,738,132.
A problem which arises with such known roll-over vent valves, especially those with a relatively large vent outlet aperture, is to ensure positive opening of the valve, either when the fuel level drops or when the vehicle and its fuel tank return to their normal position. Thus, the larger the vent outlet the greater the differential pressure acting on the valve and, in consequence, the greater the closing force effective on the valve.
Another problem which may occur with prior art valves is that pressure drop within the fuel tank may result in damaging of the fuel tank (e.g. cracking thereof). For that purpose, it has been known to form a bleed aperture permitting airing of the fuel tank, however at a significantly slow rate. Pressure drop within the fuel tank may occur, for expel as a result of increased fuel consumption (e.g. during acceleration of the vehicle) and during drop of temperature and pressure changes (e.g. change of altitude).
It has now become a demand by many manufacturers to provide fuel tanks fitted with valve means suited for rapid airing of the fuel tank upon pressure decrease in the fuel tank, at substantially high flow rates, so as to minimize the risk of damaging a fuel tank with consequential environmental issues.
It is an object of the present invention to provide an improved roll over vent valve, of the type fitted with a pressure retention device, wherein the above issues are addressed.